There exist several drop axles in the commercial vehicle freight industry. Drop axles support wheels at either end and provide clearance between the wheels for various components, such as drive shafts and discharge tubes on commercial vehicles.
Previous drop axle assemblies typically comprised formed tubes and a pair of spindles for holding wheels. The spindles were mounted to opposite ends of the tube, and the tube had formed therebetween a generally U-shaped indent to provide clearance for various components. It is desired that the spindles are coaxially aligned with each other; however, such formed-tube drop axles frequently result in misalignment between the spindles. Spindle misalignment causes accelerated tire wear and increased stresses at the intersections between axles and vehicle suspensions. One solution is to correct any misalignment by straightening the ends of the tubes after initial forming. This increases the cost to manufacture the tubes.
In an attempt to mitigate some of the disadvantages of formed-tube drop axles, manufacturers hot-form the tubes. Hot-formed tubes, however, require post-forming quenching and tempering to restore mechanical properties lost during hot-forming. The post-forming heat treatment further requires shot-blasting to remove scale, a by-product of heat treatment.
A further disadvantage to formed tubes is that forming the tubes necessarily results in thinning of the walls of the tube in high-stress regions, resulting in stress risers. Manufactures attempt to mitigate these stress risers by using thicker, heavier tubes, thereby increasing the weight and cost of their drop axles. In the commercial freight industry, increasing the weight of truck components adversely impacts fuel economy and profits.
Before forming, tubes have generally circular cross-sections. During forming, the circular cross-section is forced into an oval shape. This is often unavoidable as the material needs to stretch on the outside radii, and compress on the inside radii in order to form to the U-shaped indent. The tension on the outer radius of the tube and compression on the inner radius cause the top and bottom to be pulled together, distorting the circular cross section into an oval shape. In typical applications it is required that brackets be welded to the axle in various locations. When a bracket needs to be welded near a distorted area of the tube, custom fitting is often required to fit a bracket to a non-uniform region, adding cost to assembly.